Micromechanical component and method for producing the same

ABSTRACT

A method of manufacturing a micromechanical component having the following steps is described: providing a substrate ( 1 ); providing a first micromechanical functional layer ( 5 ) on the sacrificial layer ( 4 ); structuring the first micromechanical functional layer ( 5 ) in such a manner that it is provided with a mobilizable sensor structure ( 6 ); providing and structuring a first sealing layer ( 8 ) on the structured first micromechanical functional layer ( 5 ); providing and structuring a second micromechanical functional layer ( 10 ) on the first sealing layer ( 8 ) which has at least a covering function and is at least partially anchored in the first micromechanical functional layer ( 5 ); making the sensor structure ( 6 ) movable and providing a second sealing layer ( 8 ) on the second micromechanical functional layer ( 10 ). A corresponding micromechanical component is also described.

BACKGROUND INFORMATION

[0001] The present invention relates to a micromechanical componenthaving a substrate an a movable sensor structure in a firstmicromechanical functional layer on the sacrificial layer. The presentinvention also relates to a corresponding manufacturing method.

[0002] Although it is applicable to any micromechanical components andstructures, in particular to sensors and actuators, the presentinvention and the underlying problem are elucidated with reference to amicromechanical component, e.g., an acceleration sensor, that ismanufacturable using silicon surface micromechanical technology.

[0003] Monolithically integrated inertial sensors manufactured bysurface micromechanical technology in which the sensitive movablestructures are situated on the chip without protection (analog devices)are generally known. This results in increased expenses for handling andpackaging.

[0004] This problem may be circumvented by a sensor, the structuresmanufactured by surface micromechanics being covered by a second capwafer. This type of packaging is responsible for a large share(approximately 75%) of the cost of manufacturing an acceleration sensorby surface micromechanical. These costs arise as a result of the highsurface area requirements of the sealing surface between the cap waferand the sensor wafer and due to the complex structuring (2-3 masks, bulkmicromechanics) of the cap wafer.

[0005] The structure of a functional layer system and a method forhermetic capping of sensors using surface micromechanics is described inGerman Patent Application 195 37 814 A1. The manufacture of the sensorstructure using known technological methods is explained. The citedhermetic capping is performed using a separate cap wafer made ofsilicon, which is structured using expensive structuring processes suchas KOH etching. The cap wafer is applied to the substrate with thesensor (sensor wafer) using a seal glass. This requires a wide bondingframe around each sensor chip to ensure an adequate adhesion and sealingability of the cap. This limits the number of sensor chips per sensorwafer considerably. Due to the large amount of space required and theexpensive manufacture of the cap wafer, sensor capping incursconsiderable costs.

ADVANTAGES OF THE INVENTION

[0006] The manufacturing method of the present invention having thefeatures of claim 1 and the micromechanical component as recited inclaim 12 have the following advantages.

[0007] It builds on a known surface micromechanical method which createsepitaxial polysilicon of a thickness of at least 10 μm to form amicromechanical functional layer. No novel permeable layer is requiredbut rather known processes are used. The only novel feature is the stepto produce the sealing layers which have a sealing and levelingfunction.

[0008] The result is that the surface micromechanical method issimplified since the cap wafer is not needed due to the secondmicromechanical functional layer which performs at least one coverfunction and the structures may be contacted from above.

[0009] In addition, the functionality of the process is enhanced, i.e.,additional mechanical and/or electrical components to implement thecomponent are available to the designer. The following functionalelements in particular may be created:

[0010] a pressure sensor diaphragm in the second micromechanicalfunctional layer;

[0011] a printed conductor structure in the second micromechanicalfunctional layer which is capable of crossover with an additionalprinted conductor structure provided above the second sealing layer;

[0012] very low-resistance aluminum leads in the additional printedconductor structure provided above the second sealing layer;

[0013] a vertical differential capacitor;

[0014] additional anchor points of the structures of the firstmicromechanical functional layer in the second micromechanicalfunctional layer.

[0015] Customary IC packaging methods such as hybrid, plastic,flip-chip, etc. may also be used.

[0016] The dependent claims contain advantageous refinements of andimprovements on the object of the present invention.

[0017] According to a preferred refinement, a sacrificial layer isprovided on the substrate and the sacrificial layer is etched tomobilize the sensor structure. In a simplified version, the substratemay be provided with a sacrificial layer and the first micromechanicalfunctional layer may be provided as a silicon-on-insulator (SOI)structure.

[0018] According to another preferred refinement, the firstmicromechanical functional layer is structured in such a way that it haspassages extending to the sacrificial layer. Furthermore, the secondmicromechanical functional layer is structured in such a way that it hassecond passages extending to the first sealing layer, the secondpassages being connected to the first sealing layer by connection areas.The first sealing layer is then etched to remove the connection areasusing the second passages as etch channels. Finally, the sacrificiallayer is etched using the first and second passages connected togetherby the removal of the connection areas. This minimizes the cost of theetching processes since it is possible to etch the sacrificial layer andthe first sealing layer in one step.

[0019] Thus, etch channels running through the first and secondmicromechanical functional layer and the intermediate first sealinglayer are produced to remove the optionally provided sacrificial layer.This makes it possible to increase the thickness of the secondmicromechanical functional layer and improve its strength or stiffness.As a consequence, it is possible to span large areas and expose thecomponents to greater stress. When removing the sacrificial layer, itnot necessary to be concerned with the aluminum of the printedconductors or the like since it is not applied until a later point intime.

[0020] According to another preferred refinement, a buried polysiliconlayer is provided below the first or second micromechanical functionallayer. It is also possible to dispense with the buried polysilicon andan insulation layer lying below it since additional wiring levels abovethe sensor structure are available.

[0021] According to another preferred refinement, the first and secondsealing layer are designed substantially thinner than the first andsecond micromechanical functional layer.

[0022] According to another preferred refinement, the first and/orsecond sealing layers are provided by a nonconforming deposition in sucha manner that only the upper areas of the first and second passages,respectively, are obstructed. This reduces the etching time for removalof the sacrificial layer since only a portion of the passages isobstructed.

[0023] According to another preferred refinement, the first and/orsecond passages are designed as trenches or holes which narrow towardthe top.

[0024] According to another preferred refinement, the first and/orsecond micromechanical functional layers are made of a conductivematerial, preferably polysilicon.

[0025] According to another preferred refinement, the first and/orsecond sealing layers are made of a dielectric material, preferablysilica.

[0026] According to another preferred refinement, one or more printedconductor layers, preferably made of aluminum, are provided on thesecond sealing layer.

[0027] According to another preferred refinement, a printed conductorstructure is integrated into the second micromechanical functionallayer.

DRAWING

[0028] Exemplary embodiments of the present invention are illustrated inthe drawing and described in detail in the description below.

[0029]FIG. 1 shows a schematic cross-sectional view of a micromechanicalcomponent according to a first embodiment of the present invention in afirst process stage;

[0030]FIG. 2 shows a schematic cross-sectional view of themicromechanical component according to the first embodiment of thepresent invention in a second process stage;

[0031]FIG. 3 shows a schematic cross-sectional view of themicromechanical component according to the first embodiment of thepresent invention in a third process stage;

[0032]FIG. 4 shows a schematic cross-sectional view of themicromechanical component according to the first embodiment of thepresent invention in a fourth process stage and

[0033]FIG. 5 shows an enlarged detail of the schematic cross-sectionalview of the micromechanical component according to the first embodimentof the present invention as shown in FIG. 4.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0034] In the figures, identical reference symbols denote identical orfunctionally equivalent components.

[0035]FIG. 1 shows a schematic cross-sectional view of a micromechanicalcomponent according to a first embodiment of the present invention in afirst process stage.

[0036] In FIG. 1, 1 denotes a silicon substrate wafer, 2 a lower oxide,3 a buried polysilicon layer, 4 a sacrificial oxide, 20 a contact holein lower oxide 2 and 21 denotes contact holes in sacrificial oxide 4.

[0037] In order to manufacture the structure shown in FIG. 1, loweroxide 2 is first deposited on the entire surface of silicon substratewafer 1. In a subsequent step, polysilicon is deposited and structuredto produce printed conductors in buried polysilicon layer 3.

[0038] Subsequently, sacrificial oxide 4 is applied to the entiresurface of the overall structure using, for example, a low-temperatureoxide (LTO) method or a tetraethyl orthosilicate (TEOS) method. Thencontact holes 20 and 21 are created at the intended locations usingconventional photomethods and etching methods.

[0039]FIG. 2 shows a schematic cross-sectional view of themicromechanical component according to the first embodiment of thepresent invention in a second process stage.

[0040] In addition to the reference symbols already introduced in FIG.2, 5 denotes a first micromechanical functional layer in the form of anepitaxial polysilicon layer, 6 a sensor structure (comb structure) to bemobilized later, 7 trenches in first micromechanical functional layer 5,8 a first sealing oxide (LTO, TEOS or the like), 9 plugs in trenches 7made of sealing oxide 8, 16 oxide connection areas for the latersacrificial oxide etching and 22 contact holes in sealing oxide 8.

[0041] To manufacture the structure shown in FIG. 2, epitaxialpolysilicon is first deposited in a known manner to form firstmicromechanical functional layer 5 and micromechanical functional layer5 is structured to form sensor structure 6 to be mobilized and trenches7.

[0042] This is followed by a refill process to seal trenches 7 usingsealing oxide 8 and subsequent optional planarization. Although it isnot mentioned explicitly below, such planarization may in principle beperformed after each layer deposition on the entire surface.

[0043] In the example shown, the refill is not complete but rathercovers 100% of the underlying structure upward only and also provides aseal. This is shown in greater detail in FIG. 5.

[0044] A process follows to form contact holes 22 by conventionalphotomethods and etching methods. These contact holes 22 are used toanchor second micromechanical functional layer 10 to be applied later(see FIG. 3) and to limit oxide connection areas 16 for latersacrificial oxide etching.

[0045]FIG. 3 shows a schematic cross-sectional view of themicromechanical component according to the first embodiment of thepresent invention in a third process stage.

[0046] In addition to the reference symbols already introduced in FIG.3, 10 denotes a second micromechanical functional layer in the form ofan epitaxial polysilicon layer and 11 denotes trenches in secondmicromechanical functional layer 10.

[0047] To form the structure shown in FIG. 3, second micromechanicalfunctional layer 10 is deposited in a manner similar to firstmicromechanical functional layer 5 as a stable sealing layer forunderlying sensor structure 6. In addition to this sealing function,second micromechanical functional layer 10 may of course also be usedfor contacting, as a feed, as an upper electrode, etc. for thecomponent. This layer 10 is then structured to produce trenches 11 whichare later required together with trenches 9 for the sacrificial oxideetching.

[0048]FIG. 4 shows a schematic cross-sectional view of themicromechanical component according to the first embodiment of thepresent invention in a fourth process stage.

[0049] In addition to the reference symbols already introduced in FIG.4, 13 denotes a second sealing oxide (LTO, TEOS or the like), 14 acontact hole in sealing oxide 13, 15 a printed conductor level made ofaluminum which is connected to second micromechanical functional layer10 via contact holes 14.

[0050] Starting from the process stage shown in FIG. 3, the followingsteps are carried out to achieve the process stage according to FIG. 4.First, sealing oxide 8 is etched to remove oxide connection areas 16using second trenches 11 as etch channels. Sacrificial layer 4 is thenetched using first and second trenches 7, 11 connected together byremoving connection areas 16 as etch channels. A long sacrificial oxideetching is possible since no aluminum is present on the surface at thistime.

[0051] In a subsequent process step, a second refill process formssecond sealing oxide 13, this deposition also not being a conformingdeposition but rather only the surfaces of trenches 11 are occluded.This is illustrated in greater detail in FIG. 5. The internal pressureor internal atmosphere contained in sensor structure 6 is a function ofthe process conditions of the refill process. These parametersdetermine, e.g., the damping of the sensor structure.

[0052] Second sealing oxide 13 is then structured to form contact holes14 and printed conductor level 15 made of aluminum is deposited andstructured.

[0053] Although the present invention has been described above on thebasis of a preferred exemplary embodiment, it is not limited to it butinstead is modifiable in a variety of ways.

[0054] In particular, any micromechanical base materials such as, e.g.,germanium may be used and not only the silicon substrate cited as anexample.

[0055] Also, any sensor structures may be formed and not only theacceleration sensor illustrated.

[0056] Although not shown in the figures, trenches 7 and 11 may bedesigned to narrow toward the top in order to promote the non-conformingdeposition of first and second sealing layers 8, 13.

[0057] The layer thicknesses of first and second micromechanicalfunctional layer 5, 10 may be varied by the epitaxial and planarizationprocess in a simple manner since the sacrificial layer etching is not afunction of the permeability of the second micromechanical functionallayer.

[0058] Of course, the micromechanical functional layer/sealing layersequence may be repeated and it is also possible to provide a buriedprinted conductor under each micromechanical functional layer above theunderlying micromechanical functional layer.

[0059] Finally, it is also possible to apply additional wiring levelsmade of aluminum or other suitable metals with dielectric lying betweenthem.

[0060] It is also possible to planarize the individual levels usingchemical-mechanical polishing, for example, in a single polishing step,preferably only for the second sealing level.

What is claimed is:
 1. A method of manufacturing a micromechanicalcomponent including the steps: providing a substrate (1); providing afirst micromechanical functional layer (5) on a sacrificial layer (4);structuring the first micromechanical functional layer (5) in such a waythat it has a mobilizable sensor structure (6); providing andstructuring a first sealing layer (8) on the structured firstmicromechanical functional layer (5); providing and structuring a secondmicromechanical functional layer (10) on the first sealing layer (8)which has at least a covering function and is at least partiallyanchored in the first micromechanical functional layer (5); making thesensor structure (6) movable; and providing a second sealing layer (13)on the second micromechanical functional layer (10), the first andsecond sealing layers (8, 13) being designed substantially thinner thanthe first and second micromechanical functional layer (5, 10).
 2. Themethod as recited in claim 1, characterized by the steps: providing asacrificial layer (4) on the substrate (1), and etching the sacrificiallayer (4) to make the sensor structure (6) movable.
 3. The method asrecited in claim 1 or 2, characterized by the steps: structuring thefirst micromechanical functional layer (5) in such a way that it hasfirst passages (7) extending to the sacrificial layer (4); structuringthe second micromechanical functional layer (10) n such a way that ithas second passages (11) extending to the first sealing layer (8), thesecond passages being connected to the first passages (7) by connectionareas (16) of the first sealing layer (8); etching the first sealinglayer (8) to remove the connection areas (16) using the second passages(11) as etch channels; and etching the sacrificial layer (4) using thefirst and second passages (7, 11), connected to each other by removingthe connection areas (16), as etch channels.
 4. The method as recited inclaim 1, 2 or 3, wherein a buried polysilicon layer (3) is providedbelow the first and second micromechanical functional layer (5, 10). 5.The method as recited in one of the preceding claims, wherein the firstand/or second sealing layers (8, 13) are provided by a non-conformingdeposition in such a way that only the upper areas of the first andsecond passages (7, 11) are occluded.
 6. The method as recited in claims3 through 5, wherein the first and/or second passages (7, 11) aredesigned as trenches or holes which narrow toward the top.
 7. The methodas recited in one of the preceding claims, wherein the first and/orsecond micromechanical functional layers (5, 10) are manufactured from aconductive material, preferably polysilicon.
 8. The method as recited inone of the preceding claims, wherein the first and/or second sealinglayers (8, 13) are manufactured from a dielectric material, preferablysilica.
 9. The method as recited in one of the preceding claims, whereinone or more printed conductor layers (15), preferably made of aluminum,are provided on the second sealing layer (13).
 10. The method as recitedin one of the preceding claims, wherein a printed conductor structure isintegrated into the second micromechanical functional layer (10).
 11. Amicromechanical component comprising: a substrate (1); a movable sensorstructure (6) in a first micromechanical functional layer (5) situatedabove the substrate; a first sealing layer (8) on the firstmicromechanical functional layer (5) which is at least partiallystructured; a second micromechanical functional layer (10) on the firstsealing layer (8) which has at least a covering function and is at leastpartially anchored in the first micromechanical functional layer (5);and a second sealing layer (8) on the second micromechanical functionallayer (10), wherein the first and second sealing layer (8, 13) aresubstantially thinner than the first and second micromechanicalfunctional layer (5, 10).
 12. The micromechanical component as recitedin claim 11, wherein the movable sensor structure (6) is situated abovea sacrificial layer (4) located on the substrate (1) and is mobilized byat least partial removal of the sacrificial layer (4).
 13. Themicromechanical component as recited in claim 12, wherein the firstmicromechanical functional layer (5) has first passages (7) extending tothe depth of the sacrificial layer (4); the second micromechanicalfunctional layer (10) has second passages (11) extending to the depth ofthe first sealing layer (8); and the first and second passages (7, 11)are connected to each other by removed connection areas (16) of thefirst sealing layer (8).
 14. The micromechanical component as recited inclaim 11, 12 or 13, wherein a buried polysilicon layer (3) is providedbelow the movable sensor structure (10) between the sacrificial layer(4) and the substrate (1).
 15. The micromechanical component as recitedin one of claims 11 through 14, wherein the first and/or second sealinglayer (8, 13) has plugs (9, 9′) for sealing corresponding first andsecond passages (7, 11).
 16. The micromechanical component as recited inone of claims 13 through 15, wherein the first and/or second passages(7, 11) are trenches or holes which narrow toward the top.
 17. Themicromechanical component as recited in one of claims 11 through 16,wherein the first and/or second micromechanical functional layer (5, 10)is manufactured from a conductive material, preferably polysilicon. 18.The micromechanical component as recited in one of claims 11 through 17,wherein the first and/or second sealing layers (8, 13) are manufacturedfrom a dielectric material, preferably silica.
 19. The micromechanicalcomponent as recited in one of claims 11 through 18, wherein one or moreprinted conductor layers (15), preferably made of aluminum, are providedon the second sealing layer (13).
 20. The micromechanical component asrecited in one of claims 11 through 19, wherein the secondmicromechanical functional layer (10) has a printed conductor structure.21. The micromechanical component as recited in one of claims 11 through20, wherein the second micromechanical functional layer (10) has adiaphragm structure.